As one of damper-type seismic response control devices useful in reducing shaking of a structure, there is a variable damping device (as disclosed in Japanese Patent Laid-open No. 11-336366, for instance) or the like structured so that a valve opening of an on-off control valve is controllable in two stages so as to be switched between a full open position and a full closed position.
The above hydraulic damper has a basic structure as shown in the prior art drawings of FIGS. 11–14, specifically, includes a cylinder 2, a double rod-type piston 3 movable in a reciprocating manner within the cylinder 2, hydraulic chambers 4, 4 provided at the opposite sides of the piston 3, an on-off control valve 6 provided in a passage 5 for connecting both the hydraulic chambers, and other components. This hydraulic damper causes the on-off control valve (electromagnetic valve) 6 to be on-off controlled in two stages so as to be switched between the full open position and the full closed position with supply of control current from a controller 7, and thereby allows a damping coefficient of a hydraulic damper 1 to be switched in two stages, that is, between a maximum value Cmax and a minimum value Cmin.
Thus-structured hydraulic damper 1 is mounted between stories of a structure through a structural component such as a brace as shown in FIG. 12. Thus, mechanical characteristics of a device part including the brace are represented as Maxwell-type model configured so that a spring and a dashpot are joined in series as shown in FIG. 13.
The device of FIG. 11 performs large energy absorption as shown in FIG. 14 by switching the damping coefficient of the device, that is, the valve opening of the on-off control valve 6 at a maximum point of amplitude of vibrations, and attains a reduction of vibrations of the structure. In FIG. 14, a load L of the hydraulic damper is scaled at a vertical axis, and a story deformation (deformation between Maxwell-type model ends) δ is scaled at a horizontal axis. In addition, a portion plotted by a broken line represents a result of energy absorption using a conventional damper D0 whose damping coefficient is constant, while a portion plotted by a solid line represents a result of energy absorption using a damping coefficient switching-type damper D1. Further, control of the valve opening C will do only in two stages so as to be switched between extreme positions such as the full closed position and the full open position. Thus, the device of FIG. 11 may have a more simplified structure as compared with a device (as disclosed in Japanese Patent Publication No. 7-45781, for instance) structured so that the valve opening is variably-controllable in a continuous manner.
However, the conventional device as described above requires an uninterruptible power supply unit and a special-purpose power supply wiring, because of indispensable use of electric components such as a sensor, a controller and an electromagnetic valve. In addition, the above electric components include those needing to be exchanged regularly, so that the above conventional device brings about a need for a cost involving a maintenance cost.
The present invention is conceived in order to solve the above problems, and an object thereof is to provide a variable damping-type hydraulic damper, more specifically, a damping coefficient switching-type hydraulic damper, which may automatically switch a damping coefficient without needing supply of energy from the outside at all, and also may always surely exert an energy absorption capacity greater than that of a typical hydraulic damper.